Junjie Wang

Tsinghua University | TH · Department of Civil Engineering

One of the most prevalent causes of reinforced concrete (RC) structural deterioration is chloride-induced corrosion. This paper is concerned with a novel approach to assess the chloride ingress process for coastal concrete structures under consideration of environmental effects. Firstly, the chloride diffusion process model for one-dimensional (1-D...

Cement–asphalt mortar (CAM) has been widely used as a cushion layer in prefabricated concrete slab tracks. However, the deformation and failure of different CAMs under compression are scarcely understood. In this study, therefore, we studied the compressive deformation and failure modes of CAMs with different asphalt–cement ratios (A/Cs or m(A)/m(C...

Hydrated cement paste can be recycled by thermal activation as an alternative binder with low energy consumption and carbon dioxide emissions during production. This investigation focuses on the microstructure and phase transformation (dehydration) of GGBS/OPC blended paste (the precursor) at elevated temperature up to 850 ◦C, and the rehydration m...

Effective improvement of the frost resistance of concrete in cold regions is critical for the durability of airport pavement concrete in plateau. This paper intends to contribute to a better knowledge of the effects of combined air-entraining superplasticizer and surface treatments on the resistance against freezing-thawing and salt freezing. First...

This paper investigates the long-term performance of structural concretes in China southeast coastal area, the city of Shenzhen, exposed to atmosphere and chlorides. The structural concretes, incorporating large quantity of supplementary cementitious materials (SCM), were among the first massive application of such mixtures in construction in China...

This paper focuses on improving the flexural behavior of steel fiber-reinforced beams with continuously graded structure. Successive vibrating after casting is assumed to be a feasible way to produce graded fiber-reinforced beams (GFRBs), resulting in fibers purposefully distributed in the tensile region. The fiber orientation and distribution are...

This paper intends to contribute to a better knowledge of the dehydration and rehydration of blended SCMs(SF, FA, GGBS, LS)-cement pastes. To this end, a comprehensive experimental program combining QXRD, TG, SEM, isothermal calorimetry, MIP and mechanical tests was performed. The thermal activation temperature (TAT) has a significant influence on...

A complete durability database that provides consistent, reliable information is of great significance for concrete durability analysis. The critical challenge is that most durability databases are quite site-specific. When analyzing a local site, a model developed from the generic database may not be fully applicable to a local site. On the other...

One of the most prevalent causes of reinforced concrete (RC) structural deterioration is chloride-induced corrosion. This paper aims to provide a comprehensive insight into the environmental effect of RC’s chloride ingress process. The first step is to investigate how relative humidity, temperature, and wind influence chloride ingress into concrete...

Seawater can be used as mixing water for concrete with no steel reinforcement in some areas with difficult access to fresh water. Diatoms such as Phaeodactylum tricornutum are among the most abundant micro-organisms living in seawater, and they could be unavoidable when collecting seawater. In fact, diatoms can provide bio-SiO2 and bio-CaCO3 source...

Airport pavement concrete often suffers from freeze–thawing damage in high latitude and cold areas. In addition, the use of aircraft deicer makes the airport pavement concrete suffer from salt-freezing damage. To improve the durability of airport pavement concrete, modified polyester synthetic fiber (FC), cellulose fiber (CF), and basalt fiber (BF)...

The cement industry is currently faced with the great challenge of reducing its vast carbon footprint toward sustainability. With the findings on the rehydration behaviors of thermal-activated hardened cement paste, cement, the ‘glue’ of concrete, originally considered a non-renewable resource, now could complete a closed-loop of its whole life cyc...

CSA cement is usually used in grouting materials because of its fast setting and high early strength properties. This paper focuses on the effects of sodium sulfate and potassium sulfate on the hydration mechanism and properties of calcium sulfoaluminate (CSA) cement based double liquid grouting materials (DLGM). A comprehensive experimental progra...

This paper reviews the technical aspects related to the long-term field exposure practice in marine environments, based on the return of experiences of major marine exposure sites in world-wide scope. The long-term exposure practice helps both the research on durability mechanisms of structural concretes under real environments and the calibration...

With global concerns over increasing CO2 emissions, many countries have set up different strategies to achieve net zero CO2 emissions [...]

With the advantages of rapid setting, high strength and durability properties, calcium sulfoaluminate (CSA) cement is usually used as rapid repairing materials and grouting materials in building and other engineering projects. In order to improve the physical properties of CSA grouting materials, the effect of adding sodium aluminate and quicklime...

Chloride diffusion coefficient of concrete is a critical parameter indicating a durability property of steel-reinforced concrete elements in chloride-laden environments. However, chloride diffusion tests of concrete could take months or even years to finish in order to obtain the steady state chloride diffusion coefficient (Dss). Most engineers hav...

Using recycled concrete aggregate as substitution for natural aggregate in geopolymeric concrete to produce geopolymeric recycled aggregate concrete (GRAC), is becoming a desirable solution to handle the huge amount of construction and demolition waste, meanwhile, can harness the eco-friendly benefits from geopolymer binders. This study aims to inv...

Aggregate micro fines (AMF) were usually included in the machine-made sand during the stone breaking process. Different AMF contents could be included in different batchs of machine-made sand, and thus causing different concrete properties, like the volume stability. In order to explore the influence of AMF contents in machine-made sand on volume s...

The paper studied the effect of pre-carbonation on the C–S–H structure and investigated the positive effect of pre-carbonation on enhancing the stability of cement paste at high temperatures. OPC samples with a w/c of 0.45 were precarbonated under 20% CO2, 80% RH, and 30 °C for one week. By comparing the performance of pre-carbonation cement paste...

Sludge ceramsite recycled concrete (SCRC) is made from sludge ceramsite and recycled fine aggregate (RFA) and is expected to be an eco-efficient lightweight concrete. The SCRC in this study was produced by incorporating sludge ceramsite, RFA and ground granulated blast-furnace slag (GGBS) as a replacement for coarse natural aggregate, natural sand...

In order to improve the early age strength of ordinary Portland cement-based materials, many early strength agents were applied in different conditions. Different from previous research, the nano calcium silicate hydrate (C-S-H) particles used in this study were synthesized through the chemical reaction of CaO, SiO2, and H2O under 120 °C using the...

The application of seawater as the mixing water in concrete production could mitigate the increasing demand for fresh water in concrete production associated with the continuously increasing offshore infrastructures. Understanding the key factors that influence the properties of seawater-mixed cementitious materials could promote the application of...

Machine-made sand (MS) has become a hot topic in construction materials due to the depletion and scarcity of natural river sand. Aggregate micro fines (AMF) of varied contents were included in MS during the manufacturing process. To quantify the filling role of AMF in MS mortars, a physical packing model together with the related mathematical model...

Using fly ash, ground granulated blastfurnace slag (GGBS) and recycled aggregates made from construction and demolition (C&D) wastes to produce concrete is a promising technology. However, due to existence of the defects in the recycled aggregates, the prepared concrete usually exhibits poor physical properties. In order to modify these defects, fl...

To reduce solid waste discharges into environment and virgin resource consumptions in construction, waste seashells from seafood and aquaculture industry were recycled into powder form and reused in cementitious construction materials. This work aimed to use this biologically renewable waste material as a possible alternative to the nonrenewable li...

Chloride transport is an important subject for the durability of steel-reinforced concrete structures in chloride-laden environments. There are several different types of tests for determination of the chloride-transport properties of concretes. The understanding of the differences between these tests is critical for choosing the most suitable type...

Converting construction and demolition waste into aggregates for concrete is a promising technology, which can reduce environmental pollution and the consumption of raw materials. The purpose of this research is to investigate the combined effects of steel fibres and silica fume on the fracture behaviour of recycled aggregate concrete (RAC) exposed...

Bicarbonates can be used as accelerators to enhance the early age properties of cementitious materials. Bicarbonates like KHCO3 and NaHCO3 could form strong alkali (KOH, NaOH) and cause potential risk of alkali-silica reaction. Ca(HCO3)2 could serve as a better accelerator than these bicarbonates because of formation of CaCO3 and Ca(OH)2, which are...

Reuse of construction and demolition (C&D) wastes is essential for the protection of environment and a sustainable way for recycled materials. However, the recycled aggregate concrete with Ordinary Portland cement (OPC) paste usually had worse physical properties than the normal concrete. In this study, GGBS/metakaolin based geopolymer matrix was u...

The use of recycled aggregates in lightweight concrete is a sustainable solution to address solid wastes. This technology reduces the detrimental impacts of solid waste on the environment and addresses the shortage of natural resources. This study aimed to develop lightweight green concrete incorporating sludge ceramsite, recycled fine aggregate (R...

The production of ordinary Portland cement (OPC) is responsible for a significant part of global CO 2 emission. For decades, the raw material and high burn temperature (up to 1500 °C) for OPC production have not been changed to reduce the CO 2 emission significantly. In order to reduce the CO 2 emission for cement production, two types of recycled...

The production of ordinary Portland cement (OPC) is currently responsible for 8-9% of the global CO2 emissions. To reduce the consumption of OPC, different mineral additives have been frequently used as the cement replacements. The carbonate systems in the nature have been creating various forms of CaCO3 minerals, which can sustain the continuation...

With the depletion and increasing demand of river sand, machine-made sand could be used more and more in concrete. In order to improve the properties of machine-made sand concrete, the effects of the aggregate micro fines (AMF) content, aluminum sulfate, and polypropylene fibers (PPF) on the slump, compressive strength, water permeability, and the...

The chloride diffusion coefficient is directly related to the property of concrete to resist the ingress of chloride ions and it is a decisive factor for the durability of reinforced concrete subjected to the chloride environment. The conventional chloride diffusion test requires considerable time to attain a steady-state chloride flow across the s...

Reuse of recycled aggregates (RA), which are from construction and demolition wastes, and fly ash and ground granulated blast furnace slag (GGBS), which are from industry by-products, in geopolymeric recycled aggregate concrete (GRAC) could provide a sustainable solution to deal with the increasing construction waste and to reduce the CO2 emission...

There is a constant drive for the development of ultra-high-performance concrete using modern green engineering technologies. These concretes have to exhibit enhanced durability and incorporate energy-saving and environment-friendly functions. The object of this work was to develop a green concrete with an improved sulfate resistance. In this new t...

Grouting materials are used frequently in grouting reinforcement projects, such as mining and coastal engineering. Double liquid grouting materials are mostly used because of the fast setting and high early strength properties when the two slurries are mixed together but high fluidity when the two slurries are separated. In our study, double liquid...

Carbonates and bicarbonates are two groups of accelerators which can be used in sprayed concrete. In this study, the effects of the two accelerators sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) (0%, 1%, 2%, 3%, and 4% by weight of ordinary Portland cement OPC) on the properties of OPC paste were compared. The results show that both of...

This work introduces a cleaner production practice of transforming waste seashells into new minerals for sustainable cementitious materials. Waste seashells were recycled into fine powder through regular crushing and ball-milling processes. Multi-scale studies characterized systematically the reaction mechanisms of waste seashell powder in ordinary...

The freshwater consumption in concrete production has been notably increased, owing to the worldwide demand from the construction sector for the industrial and urban developments. To meet the requirements in the long term, reconsidering the seawater usage in concrete production, as an alternative to freshwater, perhaps can be a sustainable solution...

The practices of mineral additions to ordinary Portland cement have become increasingly important for the sustainable development in high performance cementitious materials. One key consideration for the blended formulations focuses on the effects of mineral additives/fillers on the rheological behaviours of the fresh mixtures. In this investigatio...

Geopolymer binder and recycled aggregates are considered as the two important sustainable ingredients in concrete production. Ground granulated blast furnace slag (GGBS) and fly ash combination based geopolymeric recycled aggregates concretes (GRAC) were prepared as a substitution of normal concrete in order to reduce the consumption of ordinary Po...

The use of recycled concrete aggregates in structural concrete is a sustainable solution to reduce the extraction of natural resources and the detrimental impacts of waste concrete to the environment. The present study aimed to assess the compressive and flexural behaviour of recycled aggregate concrete (RAC) and normal concrete (NC) modified with...

Prediction of chloride ingress is very important for the durability of reinforced concrete structures in chloride-laden environments, especially for concrete with cracks. It is expected that the chloride diffusion coefficient of a crack ismuch higher than that of the uncracked part in concrete. A single crack in concrete can be a shortcut for chlor...

Chloride-induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability, but most previous research projects and case studies have focused on concretes without cracks or not subjected to any structural load. Although it has been recognised that structural cracks do influence the chloride transpor...

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the...

The chloride-induced corrosion of steel is a serious problem affecting the durability of reinforced concrete structures. Cracks may facilitate the ingress of chlorides into concrete and thus accelerate the corrosion process. However, different opinions on the effect of cracks on corrosion of steel were found in the literature. Two aspects existed a...

Chloride-induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability and it has been studied for decades, but most of them have focused on concrete without cracking or not subjected to any structural load. In fact, concrete structures are subjected to various types of loads, which lead to crac...

Chloride-induced corrosion of steel in concrete is one of the most important durability and safety concerns for reinforced concrete structures. To study chloride ingress into concrete is thus very important. However, most of the researchers focus on the studying chloride ingress through concrete samples without any loading. In reality concrete stru...

Chloride-induced corrosion of steel is one of the most commonly found problems affecting the durability of reinforced concrete structures in both marine environment and where de-icing salt is used in winter. As the significance of micro-cracks on chloride induced corrosion is not well documented, 24 reinforced concrete beams (4 different mixes - on...

Phosphorous slag (PHS), ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as replacements of Portland cement to modify the microstructure of recycled aggregate concrete (RAC). A new manufacturing method named “W3T4” was proposed to improve the performances of interfacial transition zone (ITZ) between recycled aggregate and mort...

Introduction The water absorption characteristic of concrete is very important in the context of durability of concrete infrastructure. Most of the previous research projects in this respect have focused on 'laboratory' concretes that are usually not cracked or not withstanding any structural loading [1-4]. In reality, microcracking can easily deve...

Chloride induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability. The penetration of chlorides into concrete has been studied for decades, but most of them have focused on concrete without cracking or not subjected to any structural load. The chloride ingress into concrete under service lo...

A three-part model (mortar, original concrete and ITZ) was established in this study to analyze the chloride coefficient of the new interfacial transition zone (ITZ) in recycled aggregate concrete (RAC). Based on this model, a formula for calculation was derived from the chloride transport characteristics in the steady state. Two types of RAC were...

The interfacial transition zone （ITZ） is the weakest part in concrete. To enhance its properties, a new mixing method named ‘W3T4’ was proposed to modify the ITZ in recycled aggregate concrete (RAC). It involved three parts of adding water, which include the water in pre-wetting phase, and four stages of mixing procedures during making RAC. The imp...

To improve the performance of recycled aggregate concrete (RAC) and make an effective use of industrial waste, superfine phosphorous slag (PHS) were adopted as cement replacement in this study to modify the RAC. The influences of PHS on the mechanical properties and durability of RAC, mortar and interfacial transition zone (ITZ) were discussed...